|Year : 2021 | Volume
| Issue : 1 | Page : 169-174
A study on stress distribution at the bone-implant interface in platform switched short dental implants by three-dimensional finite element model
Sesha Reddy Manchala1, S Rajasekar2, Hossam Abdelatty Eid Abdelmagyd1, Ahmed Atef Aly Shon3, Venkataramana Vannala1, Shakeel S Khazi3
1 Department of Preventive Dental Sciences, College of Dentistry, Gulf Medical University, Ajman, UAE
2 Departmeat of Periodontics, Rajah Muthiah Dental College and Hospital, Chidambaram, Tamil Nadu, India
3 Department of Restorative Dental Sciences, College of Dentistry, Gulf Medical University, Ajman, UAE
|Date of Submission||16-Sep-2020|
|Date of Decision||13-Jan-2021|
|Date of Acceptance||25-Jan-2021|
|Date of Web Publication||29-Jul-2021|
Dr. Sesha Reddy Manchala
Department of Periodontics, College of Dentistry, Gulf Medical University, Ajman
Source of Support: None, Conflict of Interest: None
Aims: The authors carried out this study to analyze the pattern of stress distribution in terms of eqicrestal and subcrestal implant placement at various depths using short platform switched dental implants. Settings and Design: Modeling of the mandibular posterior molar region done with uniformly thick 1.5 mm cortical bone with an inner core of cancellous bone by three-dimensional finite element model (FEM). Implant dimensions used in the study are of length 6 mm, diameter 4.6 mm, and 3.5 mm abutments. Subjects and Methods: The applied force was 100N in an axial and oblique direction (15°, 30°) for realistic simulation. All models created by ANSYS WORKBENCH.von Mises stress is evaluation in both cancellous and cortical bone at various depths. Translations interpreted on x, y, and z-axis with ten noded tetrahedron elements with 3° of freedom per node. Results: All five position of platform switched short osseointegrated implants analyzed by FEM simulations exhibited different stress-based biomechanical behavior, dependent on bone geometry, the direction of force applied as well as on the depth of implant placement. Conclusions: Oblique forces were more deleterious than axial forces. Subcrestal implant placement resulted in reduced stress in the cortical and cancellous bone.
Keywords: Eqicrestal, finite element model, platform switched implants, short dental implants, subcrestal implants position, von Mises stress
|How to cite this article:|
Manchala SR, Rajasekar S, Abdelmagyd HA, Shon AA, Vannala V, Khazi SS. A study on stress distribution at the bone-implant interface in platform switched short dental implants by three-dimensional finite element model. J Datta Meghe Inst Med Sci Univ 2021;16:169-74
|How to cite this URL:|
Manchala SR, Rajasekar S, Abdelmagyd HA, Shon AA, Vannala V, Khazi SS. A study on stress distribution at the bone-implant interface in platform switched short dental implants by three-dimensional finite element model. J Datta Meghe Inst Med Sci Univ [serial online] 2021 [cited 2021 Sep 23];16:169-74. Available from: http://www.journaldmims.com/text.asp?2021/16/1/169/322628
| Introduction|| |
Several clinical and systematic reviews reported a high success rate for endosseous dental implants over the past decades. As a result, dental implants emerge as a natural treatment method to replace missing teeth which significantly improved overall individual health. On the contrary, many circumstances could favor implant failure among which site-related problems pose a severe threat to implant placement and failure., These failures rate attracted the interest of clinicians and researchers worldwide resulting in search for new approaches and techniques that could lead to implant success. One such attempt was the use of short dental implants.
Short dental implants stand as an alternative approach in situations such as insufficient bone volume, density, and procedures that require bone augmentation or sinus lifting in comparison to regular implants. Current terminology states that any implant <8 mm is a short dental implant. The use of short implant could be more acceptable in the coming years for an older individual, patient with chronic diseases, patients requiring less invasive procedures.
Suggestion made to use a short and wide-diameter implant to replace missing posterior teeth. However, it is recommended to apply in situations where the bone thickness is more significant than regular implant diameter. The success of short dental implants in the posterior maxilla and mandibular region exhibited mixed view. In terms of patient and clinical point of view, short dental implants offer certain advantages to their contrary.
Form a biomechanical point of view, the fundamental interaction between orderly living bone and dental implants plays an essential role in the success or failure of any implant type or design. In vitro, finite element model (FEM) design helps to understand concepts clearly for clinical application., These models distinctly have and added advantages without involving any animals or humans but at the same time provide information regarding stress, strain in the bone, and implant structures by in vivo methods. Nevertheless, it also assesses biomechanical problems before they occur.,, In the recent past, FEM gradually becomes a valuable tool in medicine and dentistry.
Bone quality and cortical bone thickness (CBT) is an essential factor determining the primary stability of implants. Lekholm and Zarb classification provided the basis for assessing bone quality for this study. CBT plays a vital role in stress or strain distribution. The authors have reported that with every increase in 0.5 mm CBT stress concentrations around implants reduced remarkably. Along with bone thickness, functional load plays a vital role in the transformation of forces from implant to bone leading marginal bone loss.
Marginal bone loss
Crestal bone loss is a crucial thing in the long-term progress and durability of dental implants. Various authors have reported crestal bone loss of 1–1.5 mm in the 1st year and 0.1 mm in the subsequent years in the past due to multiple factors. Adapting the concept of platform switch to preserve marginal bone loss functions based on the difference between implant collar and abutment. Thus, modifying the circumference of implant-abutment junction inward to the central axis of the implant.
To date, new developments in implant designs, techniques, and approaches are adapted to replace missing teeth. To examine the validity and accuracy of dental implants, concerning stress, failure rate, risk factors, biomechanics, geometry, and various numerical techniques have been developed and used. However, there are few studies evaluating stress in the platform switch short dental implants and posterior mandibular bone (D2) with subcrestal implant placement using FEM. Hence, study designed to examine the stress characteristics in the posterior mandibular region (D2). The selected implants are from Bio-horizon. Besides, another factor considered is the angulation of load. The objective of this study is to evaluate the characteristics of stress seen in the posterior mandibular bone (D2) at various depths from equicrestal to subcrestal implant placement and its relation to the angulation of force applied.
| Subjects and Methods|| |
Modeling of the mandibular posterior molar region done with uniformly thick 1.5 mm cortical bone with an inner core of cancellous bone by three-dimensional (3D) FEM. Implant dimensions used in the study are of length 6 mm, diameter 4.6 mm, and 3.5 mm abutments. The applied force was 100N in an axial and oblique direction (15°, 30°) for realistic simulation. All models created by ANSYS WORKBENCH.von Mises stress is evaluation in both cancellous and cortical bone at various depths [Table 1].
|Table 1: Average von Mises stress produced in the cortical and cancellous bone under the vertical and oblique load of 100 N|
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3D FEM geometric models are messed by Hypermesh software (ANSYS software (Analytical Graphics Inc, Canonsburg, Pennsylvania, United States)). Translations interpreted on x, y, and z-axis with ten noded tetrahedron elements with 3° of freedom per node. The model consists of (102,149 elements and 164,995) nodes for cortical bone, (132,893 elements and 198,911) nodes for cancellous bone, (14,230 elements and 24,046) nodes for implant and (9867 elements and 15,719) nodes for abutment.
Isotropic, homogeneous, and linearly elastic materials used in the model construction. Elastic properties obtained through literature and listed in the table [Table 2].
|Table 2: Mechanical properties as well as materials used in finite element model analysis|
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These finite element analysis studies include fixed boundary conditions for modelling of the mandibular posterior region. The boundary condition is the application of force and constraint. The boundary conditions constrained at a node on muscle attachment from external oblique line buccally to the mylohyoid ridge lingually.
Bone implant interface
The FEM assumed a state of optimal osseointegration resulting in an ideal fit between bone and implant. All models represent the state of osseointegration and ready to load.
This study was approved by the Institutional Ethics Committee of Gulf Medical University on 1st June 2017.
| Results|| |
Evaluation of von Mises stress done in both cortical and cancellous bone for equicrestal to subcrestally placed platform switched short dental implants under a masticatory load of 100N is represented in table [Table 1] and [Figure 1]. [Figure 2] represents the stress distribution in cortical and cancellous bone at equicreasatal position. [Figure 3] and [Figure 4] symbolize the stress in submerged short dental implants. [Figure 3] depicts subcrestal implants at 0.5 mm exhibited maximum stress in oblique direction than axial direction in both cortical and cancellous bone. However, cortical bone exhibited maximum stress in an oblique direction (30c) for 0.5 mm subcrestal implants. For cancellous bone, low-stress values are evident with subcrestal implant placement [Figure 1]. For implants placed at 1.5 mm subcrestal, they displayed least stress at (0c) after that an increase in stress oblique force (30c). As in the case of cortical bone, cancellous bone both demonstrates maximum stress in an oblique direction (30c) for subcrestal implants [Figure 4]. Cortical bone displayed the highest stress concentration at 2 mm subcrestally irrespective of angulation of force with the highest in an oblique direction [Table 1]. At equicrestal position [Figure 2], cortical bone exhibited least stress and cancellous bone exhibited maximum, stress irrespective of angulation of load. However, among subcreasatal position, maximum stress is noticed in the cortical bone at 0.5 mm subcrestal position and least at 1.5 mm in case of cancellous bone [Table 1].
|Figure 1: von Mises stress (MPa) in cortical and cancellous bone with 100N force applied at different angles|
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|Figure 2: von Mises stress (MPa) in equicrestal cortical and cancellous bone|
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|Figure 3: von Mises stress (MPa) in bone with implants placed at 0.5 mm subcresatally|
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|Figure 4: von Mises stress (MPa) in bone with implants placed at 1.5 mm subcresatal|
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| Discussion|| |
The current study focused on the analysis of stress distribution on platform switched short dental implants placed at various depths under the axial and oblique load of 100N. All five position of platform switched short osseointegrated implants analyzed by FEM simulations exhibited different stress-based biomechanical behavior, dependent on bone geometry, the direction of force applied as well as on the depth of implant placement. Nevertheless, the result of this type of study might offer a broader perceptive concerning the possible stress concentration areas, and a better explanation about the biomechanics of implant placement. The results of FEM interpreted meticulously. FEM considered the elastic properties of implant and bone as isotropic as it would not be the case.
Cortical versus cancellous
The present study displayed maximum peak stress in cortical bone with least in the trabecular region which was in agreement with previous studies.,,, At the same time subcrestal implants exhibited a biomechanical behavior different for equicrestal placement., Numerical data relieved that implant diameter plays a vital role than implant length leading decreased crestal bone loss which as consistent with our study.,,, This could be due to larger implant diameter as it leads to greater bone-to-implant contact area, higher resistance to fracture and higher initial stability, and create less stress in the bone. Nonetheless, to overcome bone loading and to enhance implant biomechanical stress-based potency, mathematical data from the current study advocate that implant diameter is more efficient criteria than implant length.,, Previous reports recommended the use of short implants to reduce implant cost and morbidity.,
Authors stated that most affected region by the occlusal load is cortical bone adjacent to the cervical area of implants no matter whichever procedure performed. The result of our study is consistent with other studies with regards to maximum stress in the cortical bone at 0.5 mm subcrestally, and least stress as it progresses to 2 mm subcrestally. It could be due to the dispersion of the masticatory load in the first millimeters around the implant neck. As a result, large implants are no more required to improve masticatory load distribution. The primary interphase between the implant and bone exhibits maximum stress that was like the observation in our study. Explained based on “engineering principle called composite beam analysis.”,
Axial versus oblique load
Our study revealed higher stress values under oblique loading conditions when compared to axial loading, both types of bone. Stress was most significant noticed in cortical bone, and the direction of force applied. The study demonstrates that higher stress concentration in an oblique direction (30c) than in axial direction regardless of the depth of implant placement. However, there was a slight decrease in stress in equicrestal position groups. Oblique forces are more destructive than axial forces and lead to greater stress accumulation around the peri-implant bone. Recommendations made to avoid or reduce oblique forces. Results from our study agree with previous studies concerning the harmful effects of an oblique load.,,
Platform switched implants mechanically switch and realign stress that eventually influences marginal bone loss around peri-implant by centralizing stress. The current study revealed shallow subcrestal placement at (1 mm) resulted in the least stress in both cortical and at (1.5 mm) in the cancellous bone which was in coherence with results of previous studies., However, cortical bone maximum stress than in cancellous bone. Authors have concluded that the platform switch concept could lead to burden the screw failure.,
Crest versus subcrestal
In the literature, we have a contradictory statement concerning subcrestal implant place. Some reported implant failure and others reported success stating reasons such as supracrestal placement would lead to oral environmental expose and bacterial contamination that lead to implant failure. Only a few researchers evaluated the concept of platform switch and short subcrestal implant placement under biomechanical conditions. This study might be the first to do so. In the present study, cortical bone stress reduced slightly at a depth of 1 mm and 1.5 mm. Its suggest that subcrestal placement results in a reduction of cortical bone stress and there reducing marginal bone loss at implant collar which is vital for implant survival and esthetics. This phenomenon attributed to different biomechanical behaviors exhibited by subcrestal implants by not engaging the crestal cortical bone. Besides, cancellous bone exhibited the least stress in subcrestal position attributed to the elastic modulus. As a result, it promotes better stress distribution. Current findings state that platform switch short subcrestal implants model results in conservation of marginal bone loss along with better stress distribution around peri-implant regions.
| Conclusions|| |
The present study demonstrated that numerical model with regards to design of implant (length, diameter) depth of placement (subcrestal), bone density (D2 bone), and force (100N) relatively affects the vector of force transmission. The diameter of the implant has more clinical significance than the length with regards to stress distribution. FEM model relieved that shallow subcrestal placed results in better stress distribution and then equicrestal placement in terms of implant depth placement. Cortical bone exhibited maximum stress in compassion to cancellous bone. Stress concentration in cortical bone was more at the implant-bone interface, whereas in the cancellous bone stress was observed more at the apical bone area.
Carefully planned and well-designed surgical protocol leads to the reduction and elimination of undue stress on implant and bone surface. FEM has been used to forecast the areas and magnitude at the bone-implant interface and to anticipate stress-bearing areas. Results of the present study applied for predicting success rate in clinical situations. Short and wide diameter implants are considered in conditions with reduced bone density. However, there need for feature studies to correlate the FEM studies to a clinical scenario.
Limitations of the study
The current study has certain limits though FEM is accurate in structure analysis:
- Bone implant contact considered as 100% osseointegrated, that would not be the case in clinical scenario
- All materials were considered isotropic and homogeneous, but, individual variations exist
- Load applied in a static condition at one point; actually, it is dynamic and varies with location and teeth
- Application of micro-movements was not possible as in realistic conditions
- Length of force applied is point of time, i.e., only once.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]